1. Field of the Invention
The present invention relates to wireless communications networks, and, in particular, to diversity techniques used for signal transmission and reception.
2. Description of the Related Art
In wireless communication systems, a transmitted signal may travel over multiple different propagation paths to a receiver antenna. Each propagation path carries a version of the transmitted signal that is altered due to factors such as the length of the path, the number of reflections in the path, and the characteristics of any objects in the path. These factors may vary from one path to the next, and, as a result, each version of the transmitted signal may arrive at the receiver antenna with a delay, a signal attenuation, and a phase shift that are different from those of the other versions. As the multiple versions arrive at the receiver antenna, they may constructively or destructively interfere with one another such that the signal received by the receiver is an amplified or attenuated version of the transmitted signal. If attenuation is relatively severe, then errors may result when decoding the received signal preventing the receiver from recovering the communicated information.
A variety of different techniques, known as diversity techniques, may be employed in a wireless communications network to improve the likelihood that the receiver will be able to recover the communicated information. In general, diversity techniques create multiple “diverse” copies of the information being communicated so that the receiver may have multiple opportunities to decode the information. The multiple “diverse” copies may be created using diversity techniques such as antenna diversity, including spatial diversity and polarization diversity, temporal diversity, and frequency diversity. If the multiple copies are sufficiently diverse (i.e., different), then the likelihood that all of the multiple copies will be attenuated in the same manner is relatively low. Thus, when one or more copies experience relatively severe attenuation, the communicated information may be recovered from the remaining copies. The receiver may combine all of the copies in an optimal way to recover as much of the communicated information as possible. Note that a wireless communications system may use multiple diversity techniques to further improve the likelihood that the receiver will be able to recover the communicated information. A discussion of different diversity techniques may be found in Tarokh, “Space-Time Codes for High Data Rate Wireless Communication: Performance Criterion and Code Construction,” IEEE Transactions on Information Theory, Vol. 44, No. 2, March 1998, pgs 744-765, the teachings of which are incorporated herein by reference in their entirety.